Systems and approaches for controlling an injection molding machine

ABSTRACT

Systems and approaches for controlling an injection molding machine having a mold forming a mold cavity and being controlled according to an injection cycle include obtaining a pattern for the injection cycle, operating the injection molding machine to inject a molten material into the mold cavity, and measuring a cavity pressure value of the mold cavity during the mold cycle. Upon measuring a nominal cavity pressure value, a pattern recognition portion of the injection cycle that is at least partially dependent on the obtained pattern commences where a driving force being exerted on the molten material is adjusted such that the measured cavity pressure matches the obtained pattern for the injection cycle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/688,482, filed on Jun. 22, 2018, the entirety of which is hereinexpressly incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to injection molding and, moreparticularly, to approaches for controlling injection molding machinesusing specific pressure profiles.

BACKGROUND

Injection molding is a technology commonly used for high-volumemanufacturing of parts constructed of thermoplastic materials. Duringrepetitive injection molding processes, a thermoplastic resin, typicallyin the form of small pellets or beads, is introduced into an injectionmolding machine which melts the pellets under heat and pressure. In aninjection cycle, the molten material is forcefully injected into a moldcavity having a particular desired cavity shape. The injected plastic isheld under pressure in the mold cavity and is subsequently cooled andremoved as a solidified part having a shape closely resembling thecavity shape of the mold. A single mold may have any number ofindividual cavities which can be connected to a flow channel by a gatethat directs the flow of the molten resin into the cavity. A typicalinjection molding procedure generally includes four basic operations:(1) heating the plastic in the injection molding machine to allow theplastic to flow under pressure; (2) injecting the melted plastic into amold cavity or cavities defined between two mold halves that have beenclosed; (3) allowing the plastic to cool and harden in the cavity orcavities while under pressure; and (4) opening the mold halves andejecting the part from the mold.

In these systems, a control system controls the injection moldingprocess according to an injection cycle that defines a series of controlvalues for the various components of the injection molding machine. Forexample, the injection cycle can be driven by a fixed and/or a variablemelt pressure profile whereby the controller uses sensed pressures at anozzle as the input for determining a driving force applied to thematerial. The injection cycle may also be controlled by a fixed orvariable screw velocity profile whereby the control senses the velocityof the injection screw as input for determining the driving speedapplied to the material.

Changes in molding conditions can significantly affect properties of themolten plastic material. As an example, material specificationdifferences between resin batches and changes in environmentalconditions (such as changes in ambient temperature or humidity) canraise or lower the viscosity of the molten plastic material. Whenviscosity of the molten plastic material changes, quality of the moldedpart may be impacted. For example, if the viscosity of the moltenplastic material increases, the molded part may be “under-packed” orless dense, due to a higher required pressure, after filling, to achieveoptimal part quality. Conversely, if the viscosity of the molten plasticmaterial decreases, the molded part may experience flashing as thethinner molten plastic material is pressed into the seam of the moldcavity. Furthermore, recycled plastic material that is mixed with virginmaterial may impact the melt flow index (MFI) of the combined plasticmaterial. Inconsistent mixing of the two materials may also create MFIvariation between cycles.

Some conventional injection molding machines do not adjust the moldingcycle to account for changes in viscosity, MFI, or other materialproperties. As a result, these injection molding machines may producelower quality parts, which must be removed during quality-controlinspections, thereby leading to operational inefficiencies. Moreover, asan injection molding run may include hundreds, if not thousands, of moldcycles, the environmental conditions of the injection molding machineare not constant across each mold cycle of the run. Thus, even if themold cycle is adapted to account for the environmental factors at theonset of the run, the changing environmental conditions may still resultin the production of lower quality parts during mold cycles executedlater in the run.

Additionally, reliance on sensed melt pressure values may result ininconsistently molded parts. For example, in environments where theinjection cycle is based on a fixed melt pressure set point curve, theinjection cycle may not be capable of properly injecting materialshaving varying characteristics (e.g., regrind, biodegradable, and/orrenewable materials). Additionally, while some systems may use anadjustable melt pressure set point curve, these systems are oftentimesincapable of maintaining material tolerances when materialspecifications (e.g., viscosity and part density) do change. As aresult, these systems may produce inconsistently-dimensioned parts, thusfurther increasing operational inefficiencies. These issues are furtherrealized in the conventional injection molding process of controlling byscrew velocity to a transfer position, moving the cycle from injectionto hold. For example, as viscosity decreases, the material is easier tomove. The injection portion will move the material at the same velocityas the nominal process but will control to the same hold pressurecausing a more dense part. Conversely, a higher viscosity material,after being filled at the nominal velocity, will create a less densepart, potentially under packing or creating a part out of dimensionalspecification.

SUMMARY

Embodiments within the scope of the present invention are directed tothe control of injection molding machines to produce repeatablyconsistent parts by treating an ideal cavity pressure profile as asystem input to control operation of an injection cycle. Systems andapproaches for controlling the injection molding machine include firstobtaining a pattern (e.g., a cavity pressure setpoint curve) for theinjection cycle and operating the injection molding machine to inject amolten material into the mold cavity. A cavity pressure value of themold cavity is measured during the mold cycle. Upon measuring a nominalcavity pressure value, a pattern recognition portion of the injectioncycle that is at least partially dependent on the obtained patterncommences where a driving force being exerted on the molten material isadjusted such that the measured cavity pressure matches the cavitypressure setpoint curve.

In these examples, during an injection portion of the injection cycle,the driving force being exerted on the molten material is adjustedaccording to a velocity or melt pressure control based input. The meltpressure control based input may include operating the injection moldingmachine at a substantially constant pressure value. In some examples,the injection molding machine may be operated according to a variablemelt pressure control curve, defined by changes in material meltcharacteristics.

Any number of drive mechanisms may be used to apply a pressure to themolten material. For example, an electric press, servo-hydraulic press,full hydraulic, or any other type of press may be used. In someexamples, the melt pressure control based input may be received via anozzle melt pressure transducer. The cavity pressure measurements may beobtained via a cavity pressure transducer located in or near the cavity.

In some examples, the injection portion of the injection cycle may becontrolled via a first controller, and a second controller may commencethe operations of the pattern recognition portion of the injection cycleIn some forms, upon measuring the nominal cavity pressure value, thecontrol of the injection cycle may be switched from the first controllerto the second controller. During the injection portion of the injectioncycle, the second controller may initially mirror a control voltageoutput from the first controller. This control voltage may be at leastone factor that adjusts the driving force received by the moltenmaterial (e.g., through the screw or press).

In accordance with another aspect, an injection molding machine mayinclude an injection unit and a mold forming a mold cavity, a controlleradapted to control operation of the injection molding machine accordingto an injection cycle, and first and second pressure sensors coupled tothe injection molding machine and the controller. The injection unit isadapted to receive and inject a molten plastic material into the moldcavity to form a molded part. The injection cycle includes a firstportion and a second portion, wherein during the first portion, thecontroller controls the injection unit at least partially based onmeasurements obtained from the first sensor. Upon an event occurring,the second portion of the injection cycle commences whereby thecontroller further controls the injection unit at least partially basedon measurements obtained from the second sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter that is regarded as thepresent invention, it is believed that the invention will be more fullyunderstood from the following description taken in conjunction with theaccompanying drawings. Some of the figures may have been simplified bythe omission of selected elements for the purpose of more clearlyshowing other elements. Such omissions of elements in some figures arenot necessarily indicative of the presence or absence of particularelements in any of the exemplary embodiments, except as may beexplicitly delineated in the corresponding written description. None ofthe drawings are necessarily to scale. For example, the dimensionsand/or relative positioning of some of the elements in the figures maybe exaggerated relative to other elements to help to improveunderstanding of various embodiments of the present invention.

FIG. 1 illustrates a schematic view of an example injection moldingmachine having a controller coupled thereto in accordance with variousembodiments of the present disclosure;

FIG. 2 illustrates an example injection profile for an injection moldingcycle in accordance with various embodiments of the present disclosure;

FIG. 3 illustrates a first example of a prior art injection profile foran injection molding cycle whereby a melt pressure setpoint is adjustedto account for changing material characteristics;

FIG. 4 is a second example of a prior art injection profile for aninjection molding cycle;

FIG. 5 illustrates a first example injection profile for an injectionmolding cycle utilizing pattern recognition control in accordance withvarious embodiments of the present disclosure; and

FIG. 6 illustrates a second example injection profile for an injectionmolding cycle utilizing pattern recognition control in accordance withvarious embodiments of the present disclosure.

DETAILED DESCRIPTION

Generally speaking, aspects of the present disclosure include systemsand approaches for controlling an injection molding machine where anoperational pattern (e.g., an operational curve) is obtained and used toat least partially control operation of the machine. In these systemsand approaches, the injection cycle is at least partially dependent on adesired operational pattern (i.e., in a closed loop manner) that isindicative of high quality parts that remain within desired dimensionaltolerances. Accordingly, the system can adjust operational parameters ofthe injection process as needed in order for its output to match that ofthe operational pattern. As used herein, the phrase “commencing apattern recognition portion of the injection cycle” means a controllercommences the operations that cause the injection molding machine tooperate in a manner that are dependent on the obtained operationalpattern or profile.

In some examples, the operational pattern may be in the form of anoperational curve that can be identified during the validation phase.One such example of a suitable operational curve is a cavity pressurecurve. As will be discussed in further detail below, the system mayadjust operational parameters of the injection molding machine in orderfor the output of the system to match that of the previously identifiedcavity pressure curve.

Turning to the drawings, an injection molding process is hereindescribed. The approaches described herein may be suitable for electricpresses, servo-hydraulic presses, hydraulic presses, and other knownmachines. As illustrated in FIG. 1, the injection molding machine 100includes an injection unit 102 and a clamping system 104. The injectionunit 102 includes a hopper 106 adapted to accept material in the form ofpellets 108 or any other suitable form. In many of these examples, thepellets 108 may be a polymer or polymer-based material. Other examplesare possible.

The hopper 106 feeds the pellets 108 into a heated barrel 110 of theinjection unit 102. Upon being fed into the heated barrel 110, thepellets 108 may be driven to the end of the heated barrel 110 by areciprocating screw 112. The heating of the heated barrel 110 and thecompression of the pellets 108 by the reciprocating screw 112 causes thepellets 108 to melt, thereby forming a molten plastic material 114. Themolten plastic material 114 is typically processed at a temperatureselected within a range of about 130° C. to about 410° C.

The reciprocating screw 112 advances forward and forces the moltenplastic material 114 toward a nozzle 116 to form a shot of plasticmaterial that will ultimately be injected into a mold cavity 122 of amold 118 via one or more gates 120 which direct the flow of the moltenplastic material 114 to the mold cavity 122. In other words, thereciprocating screw 112 is driven to exert a force on the molten plasticmaterial 114. In other embodiments, the nozzle 116 may be separated fromone or more gates 120 by a feed system (not illustrated). The moldcavity 122 is formed between the first and second mold sides 125, 127 ofthe mold 118 and the first and second mold sides 125, 127 are heldtogether under pressure via a press or clamping unit 124.

The press or clamping unit 124 applies a predetermined clamping forceduring the molding process which is greater than the force exerted bythe injection pressure acting to separate the two mold halves 125, 127,thereby holding together the first and second mold sides 125, 127 whilethe molten plastic material 114 is injected into the mold cavity 122. Tosupport these clamping forces, the clamping system 104 may include amold frame and a mold base, in addition to any other number ofcomponents, such as a tie bar.

Once the shot of molten plastic material 114 is injected into the moldcavity 122, the reciprocating screw 112 halts forward movement. Themolten plastic material 114 takes the form of the mold cavity 122 andcools inside the mold 118 until the plastic material 114 solidifies.Upon solidifying, the press 124 releases the first and second mold sides115, 117, which are then separated from one another. The finished partmay then be ejected from the mold 118. The mold 118 may include anynumber of mold cavities 122 to increase overall production rates. Theshapes and/or designs of the cavities may be identical, similar, and/ordifferent from each other. For instance, a family mold may includecavities of related component parts intended to mate or otherwiseoperate with one another.

The injection molding machine 100 also includes a controller 140communicatively coupled with the machine 100 via connection 145. Theconnection 145 may be any type of wired and/or wireless communicationsprotocol adapted to transmit and/or receive electronic signals. In theseexamples, the controller 140 is in signal communication with at leastone sensor, such as, for example, sensor 128 located in or near thenozzle 116 and/or a sensor 129 located in or near the mold cavity 122.In some examples, the sensor 129 is located in a manifold or a runner ofthe injection machine 100. It is understood that any number ofadditional sensors capable of sensing any number of characteristics ofthe mold 118 and/or the machine 100 may be used and placed at desiredlocations of the machine 100. As a further example, any type of sensorcapable of detecting flow front progression in the mold cavity 122 maybe used.

The controller 140 can be disposed in a number of positions with respectto the injection molding machine 100. As examples, the controller 140can be integral with the machine 100, contained in an enclosure that ismounted on the machine, contained in a separate enclosure that ispositioned adjacent or proximate to the machine, or can be positionedremote from the machine. In some embodiments, the controller 140 canpartially or fully control functions of the machine via wired and/orwired signal communications as known and/or commonly used in the art.

The sensor 128 may be any type of sensor adapted to measure (eitherdirectly or indirectly) one or more characteristics of the moltenplastic material 114. The sensor 128 may measure any characteristics ofthe molten plastic material 114 that are known and used in the art, suchas, for example, pressure, temperature, viscosity, flow rate, hardness,strain, optical characteristics such as translucency, color, lightrefraction, and/or light reflection, and the like, or any one or more ofany number of additional characteristics which are indicative of these.The sensor 128 may or may not be in direct contact with the moltenplastic material 114. In some examples, the sensor 128 may be adapted tomeasure any number of characteristics of the injection molding machine100 and not just those characteristics pertaining to the molten plasticmaterial 114. As an example, the sensor 128 may be a pressure transducerthat measures a melt pressure of the molten plastic material 114 at thenozzle 116.

The sensor 128 generates a signal which is transmitted to an input ofthe controller 140. If the sensor 128 is not located within the nozzle116, the controller 140 can be set, configured, and/or programmed withlogic, commands, and/or executable program instructions to provideappropriate correction factors to estimate or calculate values for themeasured characteristic in the nozzle 116.

Similarly, the sensor 129 may be any type of sensor adapted to measure(either directly or indirectly) one or more characteristics of themolten plastic material 114 to detect its presence and/or condition inthe mold cavity 122. In various embodiments, the sensor 129 may belocated at or near an end-of-fill position in the mold cavity 122. Thesensor 129 may measure any number of characteristics of the moltenplastic material 114 and/or the mold cavity 122 that are known in theart, such as, for example, pressure, temperature, viscosity, flow rate,hardness, strain, optical characteristics such as translucency, color,light refraction, and/or light reflection, and the like, or any one ormore of any number of additional characteristics which are indicative ofthese. The sensor 129 may or may not be in direct contact with themolten plastic material 114. As an example, the sensor 129 may be apressure transducer that measures a cavity pressure of the moltenplastic material 114 within the cavity 122. The sensor 129 generates asignal which is transmitted to an input of the controller 140. Anynumber of additional sensors may be used to sense and/or measureoperating parameters.

The controller 140 is also in signal communication with a screw control126. In some embodiments, the controller 140 generates a signal which istransmitted from an output of the controller 140 to the screw control126. The controller 140 can control any number of characteristics of themachine, such as, for example, injection pressures (by controlling thescrew control 126 to advance the screw 112 at a rate which maintains adesired value corresponding to the molten plastic material 114 in thenozzle 116), barrel temperatures, clamp closing and/or opening speeds,cooling time, inject forward time, overall cycle time, pressure setpoints, ejection time, screw recovery speed, and screw velocity. Otherexamples are possible.

The signal or signals from the controller 140 may generally be used tocontrol operation of the molding process such that variations inmaterial viscosity, mold temperatures, melt temperatures, and othervariations influencing filling rate are taken into account by thecontroller 140. Adjustments may be made by the controller 140 in realtime or in near-real time (that is, with a minimal delay between sensors128, 129 sensing values and changes being made to the process), orcorrections can be made in subsequent cycles. Furthermore, severalsignals derived from any number of individual cycles may be used as abasis for making adjustments to the molding process. The controller 140may be connected to the sensors 128, 129, the screw control 126, and orany other components in the machine 100 via any type of signalcommunication approach known in the art.

The controller 140 includes software 141 adapted to control itsoperation, any number of hardware elements 142 (such as, for example, anon-transitory memory module and/or processors), any number of inputs143, any number of outputs 144, and any number of connections 145. Thesoftware 141 may be loaded directly onto a non-transitory memory moduleof the controller 140 in the form of a non-transitory computer readablemedium, or may alternatively be located remotely from the controller 140and be in communication with the controller 140 via any number ofcontrolling approaches. The software 141 includes logic, commands,and/or executable program instructions which may contain logic and/orcommands for controlling the injection molding machine 100 according toa mold cycle. The software 141 may or may not include an operatingsystem, an operating environment, an application environment, and/or auser interface.

The hardware 142 uses the inputs 143 to receive signals, data, andinformation from the injection molding machine being controlled by thecontroller 140. The hardware 142 uses the outputs 144 to send signals,data, and/or other information to the injection molding machine. Theconnection 145 represents a pathway through which signals, data, andinformation can be transmitted between the controller 140 and itsinjection molding machine 100. In various embodiments this pathway maybe a physical connection or a non-physical communication link that worksanalogous to a physical connection, direct or indirect, configured inany way described herein or known in the art. In various embodiments,the controller 140 can be configured in any additional or alternate wayknown in the art.

The connection 145 represents a pathway through which signals, data, andinformation can be transmitted between the controller 140 and theinjection molding machine 100. In various embodiments, these pathwaysmay be physical connections or non-physical communication links thatwork analogously to either direct or indirect physical connectionsconfigured in any way described herein or known in the art. In variousembodiments, the controller 140 can be configured in any additional oralternate way known in the art.

In some examples, the controller 140 may be in the form of a first and asecond controller, each of which has similar features as those in thecontroller 140. In these examples, the first controller may control afirst portion of the injection cycle, and the second controller maycontrol a second portion of the injection cycle.

As illustrated in FIG. 2, an example injection profile 200 of aconventional injection molding cycle includes a number of distinctstages. While the illustrated example depicts a substantially constantpressure profile, other pressure profiles (e.g., a velocity controlled,high pressure injection molding process) may be used in conjunction withthe approaches described herein. In the illustrated example, the sensors128, 129 are any type of pressure sensors (e.g., gauge pressure sensors,differential pressure sensors, force collector type sensors such aspiezo resistive strain gauges, capacitive sensors, resonant sensors,thermal sensors, and/or electromagnetic sensors), and are disposed atthe nozzle 116 and at a location inside, near the inside, or on theouter wall of the mold 118. Specifically, the sensor 128 may be a nozzletransducer that senses a melt pressure of the injection machine, and thesensor 129 may be a cavity pressure transducer that senses a cavitypressure of the injection machine.

In the illustrated example, an operational pattern in the form of anideal melt pressure profile or setpoint 210 is identified and used as aninput to control operation of the injection molding machine 100. Inother words, in this example, the melt pressure setpoint 210 is used asthe input which determines how the machine 100 should operate, while thesensor 128 provides feedback to the controller 140 to determine whetheradjustments should be made to the injection cycle to match the meltpressure setpoint 210. As illustrated in FIG. 2, a melt pressure curve212 reflects the melt pressure measured by the sensor 128. Accordingly,the controller 140 may adjust the pressure exerted on the screw 112 inorder to maintain the melt pressure curve 212 to the melt pressuresetpoint 210. Depending on the type of machine 100 being used, differentvalves and/or motors may be used to maintain and/or adjust the pressureexerted on the back of the screw 112. For example, a servo motor may beused to turn the screw drive and control movement of the screw 112, aflow control valve may be used, which controls the quantity of hydraulicfluid being exerted on the screw 112, or a proportional valve may beused.

During a first stage 202, the molten plastic material 114 first fillsthe mold cavity 122. In this stage 202, the controller 140 increases themelt pressure to a substantially constant pressure value (e.g.,approximately 10,000 psi) and then causes the melt pressure to hold ator close to this pressure value while the molten plastic material 114fills the mold cavity 122. The molten plastic material 114 then enters apack/hold stage 204 where the melt pressure is maintained to ensure thatall gaps in the mold cavity 122 are back filled. In these systems, themold cavity 122 is filled from the end of the flow channel back towardsthe gate 120. As a result, molten plastic material 114 in various stagesof solidification is packed upon itself. In these approaches, the meltpressure is either raised or lowered based on the amount of cavitypressure measured. The degree of change is dependent on the amount ofcavity pressure and a multiplier, as will be discussed below, which aredetermined during process validation and adjusted as needed.

During this process, upon the mold cavity 122 being substantially and/orcompletely filled with molten plastic material 114, the pressure,measured by the sensor 129, within the mold cavity 122 will eventuallybecome a non-zero value. The time it takes for the injection cycle toreach a non-zero cavity pressure can be defined as a “step time”, whichis equal to the time required to fill the mold cavity 122 (e.g., a “filltime”) plus a process factor adjustment (“PFA”) value. PFA is amultiplier to the amount of cavity pressure measured in the mold. Ascavity pressure is measured, an adjustment to the Melt Pressure setpointtakes place based on a multiplier that is determined during thevalidation of the process (PFA). This multiplier can be adjusted asnecessary to make a quality part. In the illustrated example of FIG. 2,the overall step time corresponds to the duration of stage 202, andtherefore is intended to remain a fixed value. However, as will bediscussed, in practice, the actual step time for each injection cyclemay vary depending on material characteristics.

As illustrated by curve 220 in FIG. 2, which depicts a cavity pressuresensed by sensor 129, during the injection cycle and upon the cavitybeing substantially completely filled, the cavity pressure rapidlyincreases to a maximum value, and subsequently decreases until itreturns to a minimal value as the injection cycle is completed. Inconventional injection systems, the cavity pressure curve 220 is merelyan output of the injection system which may be used to provide datarepresentative of the quality of the injection cycle. As previouslynoted, during a validation stage, a number of varying injection cyclesare performed until a molded part having ideal and/or desirablecharacteristics is obtained. This ideal injection cycle will produce asan output a corresponding ideal pattern that is at least partially basedon the fill time, fill pressure, and material characteristics.Accordingly, once it is determined that a suitable injection cycle hasbeen performed that produces parts having suitable physicalcharacteristics, the resulting cavity pressure curve, such asillustrated cavity pressure curve 220 may be one example of an idealpattern obtained during the injection cycle that is used in subsequentinjection molding processes.

The example injection profile 200 illustrated in FIG. 2 does not accountfor changes in material properties; rather, the injection profile 200 isdriven by controlling the system to match the previously-identified meltpressure control setpoint 210. Thus, when changes to the material and/orenvironment invariably occur, the controller 140 continues to controlthe injection cycle in a manner that adheres to the fixed melt pressuresetpoint 210 (as opposed to, for example, adhering to a specified screwvelocity). In other words, the controller 140 will continue to cause thesame pressure to be exerted on the screw 112 regardless of whether themolten plastic material 114 is more or less viscous and/or has othervarying material characteristics. Accordingly, the screw velocity andthe step time become outputs of the system 100. If the molten plasticmaterial 114 has different material characteristics in these subsequentinjection cycles, the injection profile will result in a varying steptime and the mold cavity will either be over or under filled. In otherwords, while the injection profile 200 intends for the actual step timeto match the previously-identified step time, the actual step time forthe particular fill portion of the cycle may be shorter or longer thanthe previously observed step time value. Either of these conditions willnegatively impact the quality of the molded part. Although the fillstage 202 may not compensate for varying material melt characteristics,this compensation is performed in the pack/hold 204 stage of theprocess, using cavity pressure control. As seen in the pack/hold stageof the illustration, nozzle sensed melt pressure 212 becomes an outputof the system, while cavity sensed melt pressure 220, is controlled to asetpoint.

To overcome the presence of varying material and/or environmentalchanges in the system, injection profiles that adjust the injectioncycle have previously been employed, an example of which is depicted inthe injection profile 300 of FIGS. 3 and 4. In the injection profile300, the melt pressure setpoint 310 is adjustable as needed to cause theoverall step time to remain constant (i.e., to remain equal to the steptime obtained from the original/ideal injection cycle). In addition tothe overall step time remaining constant, in these examples, the ratiobetween the fill time and PFA time is also constant, thereby ensuringthat in the event the viscosity shifts, the entire mold cavity 122 willalways be filled, thereby avoiding flashing. In these examples, aconstant shear rate is maintained on the molten plastic material 114.

As illustrated in FIGS. 3 and 4, during the injection profile 300, thecontroller 140 monitors the melt pressure 312 via the sensor 128 tomaintain the same step time or fill rate. Accordingly, as the viscosityshifts, the melt pressure control compensates and adjusts the meltpressure setpoint 310. For example, as illustrated in FIG. 3, when theviscosity of the molten plastic material 114 increases, the meltpressure profile 310 shifts to an alternate melt pressure profile 310 athat operates at a higher melt pressure in order to maintain the sameamount of shear on the molten plastic material 114. Accordingly, thesensed melt pressure depicted by the melt pressure curve 312 a is higherthan the original melt pressure curve 312. Similarly, as illustrated inFIG. 4, when the viscosity of the molten plastic material 114 decreases,the melt pressure profile 310 shifts to an alternate melt pressureprofile 310 b that operates at a lower melt pressure in order tomaintain the same amount of shear on the molten plastic material 114.Accordingly, the sensed melt pressure depicted by the melt pressurecurve 312 b is lower than the original melt pressure curve 312.Additional details of approaches for automatic viscosity adjustment aredescribed in U.S. Provisional Appl. No. 62/665,866, filed May 2, 2018,and U.S. Provisional Appl. No. 62/568,548, filed Oct. 5, 2017, theentirety of which are hereby incorporated by reference.

While the injection profile 300 allows for adjustments to be made toaccount for changes in the environment and/or characteristics of themolten plastic material 114, the melt pressure is still used as thedetermining factor to drive the injection cycle. In this profile 300,after a cavity pressure is measured, the melt pressure may increase ordecrease depending on PFA, but will generally level out and remainconstant. The pressure at which it levels off is determined by the peakcavity pressure as well as the multiplier of PFA. As illustrated inFIGS. 3 and 4, when using the alternate melt pressure profiles 310 a,310 b, the resulting pattern (i.e., the cavity pressure curves 320 a,320 b, respectively) are merely an output of the injection profile 300.Each of the cavity pressure curves 320 a, 320 b have significantvariances in peak cavity pressure values and area under the curves 320a, 30 b from the previously determined ideal cavity pressure curve 320.Because the shape of the cavity pressure curves 320 a, 320 b is notidentical as changes to the melt pressure control are made, theresulting parts may not retain all dimensional tolerances and thus mayhave undesirable structural and/or other characteristics. The slightdiscrepancies between the curves may appear to be insignificant, but theresulting parts may be of substantially inferior quality, and mayinclude aesthetic and/or structural faults. Thus, while the injectionprofile 300 allows for adjustments without changing the overall process(i.e., by adjusting the melt pressure to keep the time to a nominal,measured cavity pressure consistent); this process typically is not usedon parts having critical dimensions.

Accordingly, and as illustrated in FIGS. 5 and 6, systems and approachesof the present disclosure use measurements from the sensor 129 as aninput to the injection profile 400. As previously noted, the sensor 129may be a transducer that senses changes to the cavity pressure,whereupon it may send an electrical charge that is converted to acalibrated voltage signal that the controller 140 interprets to identifya cavity pressure value.

As also previously noted, during the validation stage, an ideal patternmay be obtained upon determining an ideal injection pattern thatgenerates molded parts having suitable qualities. As used herein, an“ideal pattern” means an obtainable, desirable pattern that reliablyresults in a part that is reasonably free of defects. One example of apattern may be an ideal cavity pressure profile 420. In the injectionprofile 400, the injection molding machine 100 is operated as before toinject the molten plastic material 114 into the mold cavity 122. Theinjection cycle continues until an event, such as the detection of anominal cavity pressure, occurs. For example, during the injectionphase, the cavity pressure is continuously observed until a nominalcavity pressure value (e.g., approximately 50 psi) is measured. Thisnominal value is decided during setup of the optimal injection cycle,and is preferably a value that is substantial enough to be an indicatorof an actual increase in cavity pressure and not a gas bubble or otherdiscrepancy within the part.

Upon measuring a nominal cavity pressure value, the controller 140commences a pattern recognition portion of the injection cycle (such as,for example, a cavity pressure control portion). In this patternrecognition portion, the driving force exerted by the screw 112 isadjusted such that the measured cavity pressure 422 matches thepreviously obtained ideal pattern (e.g., the ideal cavity pressureprofile 420). In other words, the cavity pressure measured by the sensor129 becomes an input to the injection profile 400, and the controller140 adjusts the pressure exerted on the screw 112 so the measured cavitypressure 422 matches the cavity pressure profile 420. By ensuring themeasured cavity pressure 422 matches the previously identified idealcavity pressure profile 420, the machine 100 will consistently make thesame part having identical physical and structural characteristics.

In other words, as the viscosity, melt density, and/or othercharacteristics of the molten plastic material 114 shift, compensationin the injection profile 400 is required both during and after thefilling stage 402 to maintain the same molded part. In the first stage,a melt pressure control profile or setpoint 410 is used to apply theoptimal amount of pressure on the molten plastic material 114, which ismonitored and sensed via sensor 128 located at or near the nozzle 116and is depicted by line 412 in FIGS. 5 & 6. In the hold stage 404, thecavity pressure control profile or setpoint 420 is used to apply theoptimal amount of pressure on the material within the mold, which ismonitored and sensed via sensor 129 located at or near the mold cavity122.

As depicted in FIG. 6, as these variations to the molten plasticmaterial 114 occur, the controller 140 calculates adjustments in real ornear-real time that are required to maintain the melt pressure andcavity pressure profiles. During the fill stage 402, when the controller140 recognizes changes to the characteristics of the molten plasticmaterial 114, the melt pressure setpoint 410 is adjusted to adjustedmelt pressure setpoints (depicted by dotted lines 410 a and 410 b) asneeded to ensure that the cycle will reach a nominal cavity pressure atthe same time as in the ideal injection profile. Similarly, in the holdstage 404, a force exerted on the screw 112 (and/or its movement) isadjusted in real or near-real time in response to deviations in thecavity pressure profile (depicted by dotted lines 420 a, 420 b) toensure the sensed pressure curve 422 matches the cavity pressuresetpoint 420.

In some examples, and as previously noted, the controller 140 ensuresthe measured cavity pressure matches the previously identified idealcavity pressure profile 420, however in other examples, the controllermay ensure the measured cavity pressure is within a specified range(e.g., one standard deviation) of the previously identified ideal cavitypressure profile 420. In other words, the injection profile 400 closesthe loop within a certain range. For example, the controller 140 may setan upper and/or a lower limit on acceptable peak cavity pressure valueswhen compared to a peak cavity pressure value taken from the previouslyidentified ideal cavity pressure profile 420. Additionally orseparately, the controller 140 may set an upper and/or a lower limit onacceptable integral (i.e., the area below the cavity pressure curve)values when compared to an integral value derived from the previouslyidentified ideal cavity pressure profile 420. In one example, the upperand lower limits of the measured values (i.e., the peak cavity pressureand integral values) may be within approximately 5% of the valuesderived from the previously identified ideal cavity pressure profile420. Other examples of suitable limits are possible.

It is understood that in the injection profile 400, before the sensor129 measures a nominal cavity pressure value, any type of controlprofile may be used. For example, during the first stage 402 of theinjection profile 400, the controller may control the injection profile400 in a similar manner to: a) the first stage 202 of injection profile200 (i.e., using a fixed melt pressure setpoint value); b) the firststage 302 of injection profile 300 (i.e., using a variable melt pressuresetpoint value); and/or c) using any other control profile. However, inthe illustrated example of FIGS. 5 and 6, a variable melt pressurecontrol profile is used.

As previously noted, in the injection profile 400, the controller 140switches from a melt pressure control profile to the cavity pressurecontrol profile 420 automatically. It is understood that this transitionmay occur based on the occurrence of any number of different events suchas sudden changes or specific values in one or more of the signals beingsensed by the system. Further, in some examples, the controller 140 mayincorporate machine learning techniques to automatically identifyappropriate conditions for switching to the cavity pressure profile 420.

In some of these examples, the controller 140 may be in the form of twoseparate or distinct controllers whereby a first controller isresponsible for controlling the melt pressure profile, and a secondcontroller is responsible for controlling the cavity pressure profile420. In these examples, the first controller controls the melt pressureprofile by generating an output voltage received by the screw control126. At the same time, the second controller may mirror the outputvoltage generated by the first controller, but this output voltage isnot sent to the screw control 126. Upon the operation of the patternrecognition portion of the injection cycle commencing, a “switch-over”occurs whereby the output voltage of the second controller is sent tothe screw control 126 and the cavity pressure profile 420 is used to atleast partially control operation of the injection cycle. Accordingly,the transition from the melt pressure control to the cavity pressurecontrol is seamless and the screw control 126 receives an uninterruptedcontrol signal.

In some examples, the sensor 129 may be disposed remotely from the moldcavity 122, yet may still be in communication therewith. For example,U.S. Pat. No. 15,216,762, filed Jul. 22, 2016, the entirety of which ishereby incorporated by reference, describes the use of one or moreexternal sensors as a virtual cavity sensor. Such a sensor or sensorarrangement may be used interchangeably with the sensor 129 describedherein.

The above-described approaches may be used in conjunction with anyinjection process where the previously-identified pattern is used todrive at least a portion of the injection cycle. These approaches may beused in the formation of any number of different molded partsconstructed from a variety of materials such as, for example siliconeand metal parts.

Those skilled in the art will recognize that a wide variety ofmodifications, alterations, and combinations can be made with respect tothe above described embodiments without departing from the scope of theinvention, and that such modifications, alterations, and combinationsare to be viewed as being within the ambit of the inventive concept.

The patent claims at the end of this patent application are not intendedto be construed under 35 U.S.C. § 112(f) unless traditionalmeans-plus-function language is expressly recited, such as “means for”or “step for” language being explicitly recited in the claim(s). Thesystems and methods described herein are directed to an improvement tocomputer functionality, and improve the functioning of conventionalcomputers.

What is claimed is:
 1. A method for controlling an injection moldingmachine having a mold forming a mold cavity, the injection moldingmachine being controlled according to an injection cycle, the methodcomprising: obtaining a pattern for the injection cycle; operating theinjection molding machine to inject a molten material into the moldcavity; during an injection portion of the injection cycle, adjusting adriving force being exerted on the molten material according to a meltpressure control-based input; measuring a cavity pressure value of themold cavity during the injection cycle; upon measuring a nominal cavitypressure value indicative of an actual increase in cavity pressure,commencing a pattern recognition portion of the injection cycle that isat least partially dependent on the obtained pattern, where the drivingforce being exerted on the molten material is adjusted such that themeasured cavity pressure matches the obtained pattern for the injectioncycle; wherein during the injection portion of the injection cycle, amelt pressure setpoint is adjusted to ensure the nominal cavity pressurevalue is measured at a predetermined ideal time.
 2. The method of claim1, wherein obtaining a pattern comprises obtaining a cavity pressuresetpoint curve for the injection cycle.
 3. The method of claim 2,wherein the injection portion of the injection cycle is controlled via afirst controller, and wherein the pattern recognition portion iscommenced by a second controller.
 4. The method of claim 3, furthercomprising upon measuring the nominal cavity pressure value, switchingcontrol of the injection cycle from the first controller to the secondcontroller.
 5. The method of claim 4, wherein during the injectionportion of the injection cycle, the second controller mirrors a controlvoltage output from the first controller.
 6. The method of claim 1,wherein the melt pressure control-based input comprises operating theinjection molding machine according to a variable melt pressure controlcurve.
 7. The method of claim 1, wherein the driving force being exertedon the molten material is exerted by at least one of a press, a servomotor, or a flow control valve.
 8. The method of claim 1, wherein themelt pressure control-based input is received via a nozzle melt pressuretransducer, and wherein the cavity pressure measurement is obtained viaa cavity pressure transducer.